Developing Sterile Invasives…Why Bother?

Beautiful but highly invasive winged burning bush (Euonymus alata) spreading through a Hardwick, Massachusetts woodland

Were you aware that USDA is sponsoring research at the University of Connecticut to develop sterile varieties of Winged Burning Bush (Euonymus alatus) and Japanese barberry (Berberis thunbergii) — both non-native plants spreading aggressively into natural and agricultural areas in many parts of the USA.

Sounds like a good idea, right? After all, if the plant is sterile – in other words, it doesn’t produce viable seeds or berries –  it can be safely planted without risk of its seeds being spread by birds (or wind) into other areas.

But history shows that this theory hasn’t worked well for other ornamental invasives. Sterile cultivars of the invasive purple loosestrife such as ‘Dropmore Purple’ and ‘Morden’s Pink‘ were found to eventually produce viable pollen and seed and happily cross-pollinate with the wild species.

Reversion from “sterile” to “fertile” has also been reported in a number of other plants marketed as “sterile”, including Bradford/Callery Pear (Pyrus calleryana), reported invasive from the Great Lakes south to the Gulf Coast. To quote from Jurassic Park, “Nature will find a way”.

The environmental problems caused by invasive plants spreading from home landscapes is well-known, at least by governmental agencies and ecologists, if not consumers. Both burning bush and barberry have significant negative impacts on natural systems when they grow where they don’t belong.

Although now banned for sale in many states, including Massachusetts and New Hampshire, introducing sterile cultivars are not the solution. The runaway horse left the barn years ago, and our unmanaged woodlands are now heavily infested.

Barberry spreading through a central MA woodland, spread from nearby residential plantings

Where barberry has taken over woodland areas, studies show the plant can alter the soil chemistry (pH) and increase nitrate levels, making the soil inhospitable to existing woodland trees and understory plants* who eventually decline along with the associated wildlife that depend on them.

The presence of barberry is also being linked with high numbers of Lyme Disease, a horrible disease now approaching epidemic levels in the northeast. Barberry’s thorny foliage is good cover for mice and small rodents, who researchers from the Cary Institute for Ecosystem Studies believe are the top apex of the Lyme Disease pathogen, more so even than deer.

So why do we want to continue the heavy reliance on these plants in the nursery trade? Why invest all the energy and tax dollars into development of plants that shouldn’t be growing here in the first place? Simply put, it’s about money.

Burning bush sales are said to top $38 million nationwide, and plant breeders will tell you that consumers want this plant, that they ask for it, and the work fulfills a real demand. I understand that a lot of people buy plants on impulse because of their color, or they see a plant in a friend’s yard and decide to buy it for their own property without researching it first.

But I’m willing to bet that most consumers are willing to take this advice: “Barberry is a bad choice for the environment. Plant THIS instead.” In my own experience as a garden coach, I have only had one client in 5 years that did not remove their burning bushes after I explained their impact on our natural ecosystems.

I feel quite proud that my advice has led to the removal of a couple of dozen winged burning bush from suburban Massachusetts yards. I believe that landscaping professionals have great power to influence landscaping trends, and we have a responsibility to educate consumers about the consequences of their landscaping choices.

Admittedly, the rich burgundy color of red barberry cultivars (pictured, Crimson Pygmy) are attractive in home landscapes and the birds are happy to eat the berries. But when berries are deposited in nearby woods, seedlings generally revert to the green form, which begin their stealth campaign for understory dominance.

Not all states consider invasive plants as a legislative priority at the moment, but local landscaping and nursery organizations seem to be picking up the slack. The CT Landscape & Nursery Association has implemented a voluntary phase-out of  the use of invasive Japanese barberry cultivars (but unfortunately not burning bush), and hopefully other green industry organizations will follow suit.

It also appears that our federal agencies need to re-evaluate where they are devoting their energy. The USDA web site proudly announces that sterile barberry cultivars should be available for sale within a decade. OK, but in the meantime, our remaining intact natural support systems are increasingly degraded by the continuing presence of invasives in home and public landscapes.

We need to persuade our governmental agencies to re-allocate resources to cultivating and restoring native plant populations in our natural areas, not pandering to landscaping trends.

So, for gardeners looking for alternatives to winged burning bush and invasive barberry, what can they plant that offers the same outstanding characteristics without damaging the environment?

There is a native Euonymus atropurpureus (Eastern Wahoo) that has the blazing red color of the invasive variety. Other eastern native shrubs with fiery fall foliage are Virginia Sweetspire (Itea virginica) and Highbush Blueberry (Vaccinium corymbosum).

If you enjoy the architectural shape of burning bush, plant Pagoda Dogwood  (Cornus altinifolia) or Amelanchier Shadbush (aka Serviceberry).

For the red/burgundy or gold foliage cherished in the Japanese barberry cultivars, try dark or gold-leafed cultivars of Ninebark (Physocarpus opulifolius) – pictured below.

If you’re looking for a low thorny hedging plant as living ‘barbed wire’ to keep unwanted visitors out, try the native Virginia or Carolina Rose (Rosa virginiana or carolina).

Dark-foliaged American native shrub ninebark (Physocarpus opulifolius) blooming in white snowballs on the edge of a farm pond. Shorter cultivars of ninebark are available for smaller spaces.

For lots more information about native alternatives to invasive plants, read through the NPWG  series of articles titled Plant This, Not That:

Plant This, Not That (Connecticut)

Plant This, Not That (New York)

Plant This, Not That (New Jersey)

Plant This, Not That: Native Groundcovers (Maryland)

Plant This, Not That: Native Groundcovers (North Carolina)

Plant This, Not That Creeping Bellflower (Midwest)

Plant This, Not That (California)

Plant This, Not That: Native Alternatives to Invasive Plants

Plant This, Not That: The Book

 

* Studies cited:

Changes in Soil Functions Following Invasions of Exotic Understory Plants in Deciduous Forests (Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, New Jersey 08901 USA)

The Forest Floor’s Role in the Invasion Success of Two Exotic Species, Japanese Barberry (Berberis thunbergii) and Japanese Stiltgrass (Microstegium vimineum) 

Don’t Miss! Ellen Sousa’s Book (click image for more information)

 

 

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Comments

  1. says

    A great post Ellen! Why bother indeed! When education is all that is needed. USDA ought to know better. I have many of your alternatives and love them. I am intrigued by the link to lyme with barberry. I do not have the one you mention but do have one I inherited up by the barn. It has delicate dangling pedants of yellow blooms in June. I have not seen it spreading about, but I am trying to find out which barberry it is.
    Carol Duke recently posted..Flower Hill Farm BUTTERFLIES OF 2011 ~ Favorite Viceroy

  2. says

    It seems Ellen that every house has a burning bush and/or barberry in my neighborhood. I know I have barberry that are columnar and will be replacing them…I am watching to make sure they do not spread anywhere. What does spread and is invasive in NY as well is buddleia. I am removing any I still have this year and putting in a fringe tree, serviceberry and some inkberry. I cannot see the point of planting these so-called sterile bushes when there are much more interesting plants to use. Unfortunately they do not outlaw any plants here except loosestrife because it has invaded all the wetlands. And I am not even sure they have a law against selling it in NY to be honest.
    Donna@Gardens Eye View recently posted..Seasonal Celebrations-A Dream of Spring

  3. Sue Sweeney says

    I just added your post to the CT MG’s FB post announcing the new sterile winged eponymous. I had previously posted the about the same thing on their post about the new improve Japanese barberry.

    However, you’re right it’s all money — the nursery trade in CT was strong enough to gut our invasives’ law. You’ll see – winged euonymus, the number one understory shrub issue is not banned but classified as only “potentially” invasive. http://nbii-nin.ciesin.columbia.edu/ipane/ctcouncil/invplantsCT09commonname.pdf Likewise, all variegated barberry is exempt from any ban on barberry.

    While I think the money and time should have gone into education on “why plant native”, sadly, it may be the UConn group has a point — the only way around is to feed the nursery trade (which seems unable to adapt) something they can live with.

  4. Sue Sweeney says

    BTW: nothing outshines the fall color of blueberry bushes; your birds will so appreciate the fruit; and the bush is an important butterfly larvae host.

  5. says

    This is a really great post. Replacing a non-native with the same non-native which is sterile does nothing for our very important home ecosystems. I agree there are so many alternatives to these plants and do not understand why they are still so popular. The burning bush is only nice looking in fall–it outgrows the space given to it by landscapers quickly and in the home landscapes I have seen, spreads quickly so even the homeowners do not like it anymore. I have replaced many and we do not sell it where I work. People do ask for it and we suggest native alternatives, many of those listed above and in the CT link “Plant This, Not That” you provided here. The good news is that some kids in our CT schools are learning about both barberry and burning bush from the outdoor educations teachers from kindergarten on. The teachers point it out on hikes and ask the kids to go home and tell their parents about it too. The parents that join in on these hikes are shocked when they realize they too have these plants at home. I do see landscapers embracing Itea–I see it planted in many places including strips along busy streets and parking lots, both very tough places for a plant to grow–and they are doing well.
    Diane St John recently posted..Just Say No

    • Chris Murray says

      Haven’t they read Doug Tallamy’s book, Bringing Nature Home? Even if sterile, non-native plants
      have little value for insects and wildlife and help foster the decline of biodiversity.

      I don’t know if this comment is registering.

  6. says

    Ellen
    what a great post. I agree that money would be much better spent educating people about using natives rather than working on sterile invasives! There was just an article in the journal BioScience last October about this issue. (http://www.jstor.org/pss/10.1525/bio.2011.61.10.11)
    Here is a summary.

    “Non-invasive” cultivar? Buyer beware.

    Cultivars of popular ornamental woody plants that are being sold in the
    United States as non-invasive are probably anything but, according to an
    analysis by botanical researchers published in the October issue of
    BioScience. Tiffany M. Knight of Washington University in St. Louis,
    Missouri, and her coauthors at the Chicago Botanic Garden write that the
    claims of environmental safety are in most cases based on misleading
    demographic evidence that greatly underestimates the plants’ invasive
    potential. What is more, the offspring of cultivars do not usually “breed
    true” and may be more fecund than their parents, especially if they cross
    with plants from nearby feral populations.

    Many invasive plants were once ornamental cultivars, because the
    characteristics that the “green” industry looks for are the same ones that
    make a plant potentially invasive-being adaptable to wide range of
    conditions, forming dense stands good for erosion control, and having a long
    flowering period, for example. In recent years the nursery and horticultural
    industries have responded by creating cultivars of top-selling plants that
    produce reduced numbers of viable seed and are advertized as “safe to
    natural areas.” Such cultivars of Japanese barberry, buckthorn, and burning
    bush are now widely sold, as they avoid bans on growing invasive species.

    Yet simple population modeling demonstrates that reductions of even 95
    percent in the number of viable seed will leave a long-lived species quite
    capable of spreading-and many of the new cultivars do not achieve even that
    much of a reduction. More sophisticated modeling would likely reveal even
    stronger invasive potential of the “safe” cultivars. Knight and her
    coauthors conclude that only completely sterile cultivars can be considered
    truly safe without further testing, and that other types should be tested
    for breeding true and having a low growth rate before they are sold as
    non-invasive.

    • Sue Sweeney says

      Good to know about this study — a lot of the nursery trade’s ability to gut the CT law was based on their contention that the variegated cultivars didn’t spread; otherwise you would see them in the woods, right? Seems like they all forgot about Gregor Mendel.

  7. says

    A great post. I am heartened by the news that some states have banned certain plants or are in phase-out programs. Plants like Chinese and Japanese ligustrum (privet) plague the southeast in a similar fashion. Georgia has no ban on these or others. Knowing that other states have taken at least some measures against their invasive flora gives me hope that we can introduce similar legislation. But you’re right, it’s all about the money and we have to keep that in mind as we work to convince the industry to stop growing it.
    Ellen Honeycutt recently posted..Bluets, Beauties and Bloodroot – oh my!

    • Sue Sweeney says

      So how to address the nursery industry? Money seems to be the only language that the nursery trade know – they are for profit businesses after all.

      Put all our money, and our clients’ money, into our closest local-genotype natives seller?

      It would be good to support the local nursery’s efforts (if for no other reason than to stop the waste of petroleum from people driving long distances to buy plants – I do like breathing) but almost all the “native” plants that the local nurseries have are “nativars” – very little actual environmentally usable stock.

      Part of the viscous circle is that “people plant what they see”. So every barberry in yard leads people to believe they want barberry, so that’s what the nursery man offers them because he thinks it is what they want. Almost like doctors giving unnecessary antibiotics and and plant clinics prescribing unnecessary insect treatments because they think that’s what the people want. There is some people-pleasing sociological process at work but I don’t know exactly what it is or how to change it.

      The nursery economics also consider that the barberry grows to sale size quickly in full sun (cheap), it won’t die sitting in the nursery yard for months or years (less inventory loss) , and that it is unlikely to die soon after being planted (low refunds). Further, the local seller and landscapers know what it is, how to handle it, and believe people want it. Risk-adverse behavior.

  8. says

    Ellen, This is certainly a thought-provoking post, as are all the comments. I think, as gardeners, we need to be careful what we wish for…that ‘wonderful’ plant that grows ANYWHERE is most likely invasive. While the nursery industry is cetainly powerful, if we can reduce the demand for these invasives, the supply will evetually fall. I’d like to see gardening magazines stop featuring barberry in virtually every edition. Yes, there’s small print, on a totally different page, saying it might be invasive, but still the photo is front and center enticing unsuspecting gardeners into buying it.
    Debbie Roberts recently posted..You Can Grow That ~ Connecticut

  9. says

    Hi Ellen,

    great information, applicable everywhere, to the problem plants for the area in question.

    Florida has it’s own set of “sterile” plants and the one that gets my chapter of the Native Plant Society up in arms is Mexican Petunia or Bluebells (Ruellia simplex) which they fail to remember can propogate by cuttings, so when the landscapers come along and do maintenance and drop the pieces along the roads (we all know how neat landscapers on the move are with their waste blowing in the breeze) whammo, the are out of their designed bounds.

    You sound like a great teacher of smart plant choices!
    Loret recently posted..Crap!

  10. Chandra S. Thammina Ph.D. says

    Why triploid Euonymus alatus ‘Compactus’ should be sterile and not become fertile

    The comments by Ms. Ellen Sousa bring out several important items for further discussion. Here I would like to provide some relevant information to the readers of this website.

    Item1: Are the seed producing capabilities of the Bradford cultivar of callery pear and the Dropmore Purple and Morden Pink cultivars of purple loosestrife due to their reversions to fertility from sterility?

    ‘Bradford’ of callery pear and ‘Dropmore Purple’ and ‘Morden Pink’ of purple loosestrife have been mistakenly called sterile cultivars because they appear to be infertile (no seeds produced) when grown in isolation. These plants are self-incompatible. Self-incompatible plants are not able to produce seeds when grown in isolation, that is, self-pollinated or pollinated from genetically identical plants. However, cross-pollination can make self-incompatible plants to produce seeds. Because ‘Bradford’, ‘Dropmore Purple’ and ‘Morden Pink’ cultivars planted in North American are cross-pollinated, they produce seeds. Thus, the seed producing capacity of ‘Bradford’, ‘Dropmore Purple’ and ‘Morden Pink’ observed in North America is not due to reversions from sterility to fertility. These plants were never sterile to begin with, nor there were reversions in fertility.

    If interested to learn more, you may read publications by Colautti et al. (2010), Culley and Hardiman (2007), and Lindgren and Clay (1993) listed in the end of this message.

    Item 2: Methods to produce stable sterile plants

    There are many stable sterile plant varieties being developed and used in agriculture, horticulture and forestry. Stable sterile plants can be created using different methods. One method is to use chemical or physical mutagens. Mutant plants created using this method can have point- or non-point mutations in the plant genome. Point-mutations means that there is a single nucleotide change in a gene important for fertility of the plant. Reversion can take place for point-mutations although the rate is very low or insignificant. Non-point mutations include DNA deletion or insertion, and chromosomal arrangements. Reversion rate of non-point mutations is also extremely low, lower than that for point-mutations. Thus, sterile mutant plants are normally very stable in generations. Transgenic method has also been used to produce sterile plants. The sterility resulted from sterile genes is also very stable across generations.

    Another important method for sterility is to create triploid plants. It has been well demonstrated that triploid plants are sterile (seedless) owing to uneven segregation of chromosomes during meiosis leading to abortive gamete or embryo development. Cross-pollination with other fertile cultivars of the same species will not make triploid plants fertile. Triploid plant cultivars have been developed in a large number of plant species such as watermelons, banana, apple, citrus, grapes and papaya etc. The sterility of triploid plants have also been demonstrated to be very stable across generations. Many triploid horticultural crop plants have been developed and approved to be totally sterile. For instance, Trueblood et al (2010) recently evaluated 10 triploid clones of Hypersicum androsaemum L. (a landscape plant) and documented that they are 100% sterile.

    Two well-known examples of stable triploid plants are banana and seedless watermelons. These triploid plants do not normally revert to fertile ones.

    Item 3: Triploid Euonymus alatus should be sterile, non-invasive, and stable across generations

    Triploid Euonymus alatus ‘Compactus’ should be seedless and sterile and also stable across generations. The triploid Euonymus alatus ‘Compactus’ will be evaluated and confirmed for their sterility and field performance in the next several years in Connecticut and elsewhere. Upon confirmation, these plants can be used for planting in landscape because they are unable to produce seeds or to spread.

    Triploid Euonymus alatus plant cultivars are different from self-incompatible ‘Bradford’ of callery pear and ‘Dropmore Purple’ and ‘Morden Pink’ of purple loosestrife. While self-incompatible plants can produce seeds if cross-pollinated, triploid plants will be seedless even if crossed with fertile plants. Also, triploid plants will not easily be reverted to seeded diploid plants.

    References

    Culley, T.M. and N.A. Hardiman. 2007. The beginning of a new invasive plant: A history of the ornamental Callery pear in the United States. BioScience. December 2007/ Vol. 57 No. 11: 956-964.

    Colautti, R.I., N.A. White. And S.C.H. Barrett. 2010. Variation of self-incompatibility within invasive populations of purple loosestrife (Lythrum salicaria L.) from eastern north America. Int. J. Plant Sci. 171(2): 158-166. 2010.

    Lindgren, C.J. and R.T. Clay. 1993. Fertility of ‘Morden Pink’ Lythrum virgatum L. transplanted into wild stands of L. salicari L. in Manitoba. HortScience 28(9):954.

    Trueblood, C.E., T.G. Ranney, N.P. Lynch, J.C. Neal. and R.T. Olsen. 2010. Evaluating fertility of triploid clones of Hypersicum androsaemum L. for use as non-invasive landscape plants. HortScience 45(7):1026-1028.

    Chandra Thammina Ph.D.,

    Dept. of Plant Science & Landscape Architecture,

    University of Connecticut.

  11. says

    Chandra, thank you so much for taking the time to respond to this post. It’s a small comfort to know that these shrubs you are developing will not continue to add to the problem caused by millions of burning bush shrubs planted in landscapes, spread by seed into nearby woods. I still question the long-term benefit of continuing to sell them, even if they’re no longer ecologically damaging, their continued presence as a popular landscape plant will undermine the efforts of those who are trying to promote the use of native plants as replacements for the exotic non-natives that generally support much fewer species…
    Ellen Sousa recently posted..NWF and ScottsMiracle-Gro? No!

  12. Sue Sweeney says

    Barberry and ticks: one of the many reasons to object to barberry is that studies confirm that its harbors an unusual number of deer ticks. A brainy friend of mine just pointed out that being sterile won’t affect its tick-attractant properties — so you want one in your yard?

  13. Kirk M says

    Fortunately I live in Mass where they have banned both barberry and burning bush for sale. I spent hours and hours last summer pulling up burning bush seedlings because we have an ancient one in the yard which unfortunately is holding up the fence separating my neighbors yard from my own. Once we get the money to replace the fence its HISTORY! So in the meantime I keep it pruned back as much as possible. This cuts down on the amount of seeds it produces.

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